1. Field
This invention relates to lighting devices used for general illumination purpose and constructed based on solid state devices such as Light Emitting Diodes better known as LED, which comprise LED arrays and electronic driving circuits enclosed in housings.
2. Prior Art
The use of LED lamps is a trend that continues and as the technology matures, it is expected that LED lamps will be the predominant source of artificial light for general illumination applications. LED lamps are robust solid state devices capable of lasting 50,000 hours or more of operation. The main electrical components of existing LED lighting fixtures are the LED module having the LED lamps organized in arrays and an electronic driver. Existing LED drivers are complex devices used to condition the voltage and current applied to the LED arrays based on high frequency switching of power electronic components. Because of the complexity of these drivers, they are usually the weakest link of an LED lighting system that severely limit the expected life and power ratings of the existing LED fixtures.
Existing LED drivers work by conditioning the input voltage to meet specific parameters of the LED arrays having a fixed configuration. Consequently, existing LED fixtures require a complex and frequently expensive electronic driver in order to adjust the applied voltage source to the electrical demand of a fixed LED array. Popular technologies used for manufacturing existing LED drivers are the PWM, and the buck and boost converters. The main drawbacks of these topologies are their high operating frequencies and the bottleneck limitation of supplying the electric power through a single electronic switching component. The high frequency switching allows for the use of smaller driver components facilitating the integration in a single package. However, the high frequency switching of power electronic devices, such as transistors, imposes a design burden and strict limitations on the maximum electrical power that can be delivered to the LED arrays. Furthermore, in addition to curtailing the power ratings of the LED lighting fixtures, existing driver topologies suffer from undesirable generation of electromagnetic noise, line power harmonics, low power factors, and low energy efficiencies among others.
There have been several attempts to use reconfigurable LED arrays as a way of controlling the power flow through the arrays but they have proved to be not practical and of low commercial value. For instance, the concept for using reconfigurable LED arrays is disclosed in the U.S. patent application No. 2002/0175826 A1 published on Nov. 28, 2002. This patent described a traffic light using reconfigurable LED arrays as a way of changing the array voltage rating to adjust to the power supply voltage fluctuations. As the voltage of the power supply decreases, sections of the LED array are turned off or bypassed by electronic transistors which in turn lower the voltage rating of the LED array, and vice versa. The problem with this concept is that it still uses complex electronic components and functions such as PWM to control the power flow, and when the magnitude of the applied DC voltage is lower than the rating of the array voltage some LED lamps of the array remain off, making it not suitable for portable DC applications using batteries. When the applied voltage falls below the array knee voltage, this concept does not provide a way for reconfiguring the array such that all lamps stay lit resulting in degraded illumination performance.
Another prior art disclosing reconfigurable LED arrays is the U.S. Pat. No. 7,936,135 B2 awarded on May 3, 2011. In addition to turning on and off sections of the LED arrays, this prior art also proposes changing the series-parallel connection of the LED lamps in the array. However, the solution proposed in this patent is still not practical and of low commercial value. For instance when the proposed regulation scheme maintains a constant current, some of the LED lamps are turned off as illustrated in FIGS. 1, 2, 3, 5, 6, 7, 8, and 9 of the patent. This concept is similar to the 2002 patent application mentioned above and it also suffers from the same lighting regulation problems. On the other hand, when the regulation scheme is to maintain lit all LED lamps within the array, the array current vary in a wide range as illustrated in FIGS. 4A, 4B, 4C, and 4D of the patent, generating high harmonics content and poor power factors. Furthermore, because the complexity of the driver increases with the number of LED lamps forming the array, this concept is not practical for higher number of LED lamps.
In addition to the complexity of the drivers, because the responses of the above reconfigurable LED arrays are either a constant current or currents that change wildly, the proposed LED lighting fixtures of the prior arts are considered not lineal. When these LED fixtures are connected to AC utility voltages, considerable amount of harmonics are generated.
There is a market need for a simpler LED lighting fixture having superior lighting and electrical performances at AC utility voltages with a minimum amount of electronic components for integration in a single package while maintaining higher efficiencies and life expectancies at a lower cost. There is a need for a simpler LED fixture design that allows for higher power lighting fixtures with a minimum line harmonics generation.